There are about as many animals in Gladiator as there are in Noah (another Russell Crowe glower-fest).
From the strange German shepherd-looking dog at the beginning, to the giraffes Proximo is complaining about in Africa, to the tigers Maximus encounters in the Colosseum, there's no shortage of Animal Planet goodness on display.
And while all these critters play a big role in the film, their significance differs from scene to scene. In the film's opening battle sequence, the dog that follows Maximus around, and ends up helping in battle when he's about to get stabbed, suggests that Maximus has a strong connection to the natural world (a connection emphasized also in the fact that he always rubs his hand in the dirt before a fight).
The giraffes in Africa, in contrast, are there to give us an idea of the scope or breath of the Roman Empire—it stretched from England and parts of modern-day Austria to the sands of northern Africa.
But that's not the only symbolic duty being done by these giraffes. When we first meet Proximo, he's complaining to a salesman:
PROXIMO: Those giraffes you sold me, they won't mate.
This little remark foreshadows Maximus' early days in Proximo's employ. No, it's not that Maximus also refuses to mate…but he does refuse to do what he was bought to do: fight. Maximus just stands there as Hagen hits him with a wooden sword.
The angry caged lion in Proximo's camp also symbolizes Maximus, and by extension, the other gladiators: they too are "caged" animals.
And we can't forget the angry tigers that Maximus has to deal with in Rome. The tigers, again, symbolize the extent of Rome's influence (there ain't no tigers in Italy). But they also are symbolic of Rome's depraved appetite for brutality (the tigers are there to kill gladiators, after all), and the dangerous odds Maximus has to face both in the arena and out of it.
Ugh. We hope that Maximus gets to snuggle some puppies or baby sloths in the afterlife.